Debra Milke was back in a Phoenix courtroom Tuesday, facing another legal battle after spending decades behind bars.

Milke, 50, has already spent more than two decades on Arizona’s death row after being convicted of murder in the 1989 death of her son, Christopher, 4.

Prosecutors convinced a jury in 1990 that Milke hired two men to take the boy into the desert and shoot him after telling her son he was going to see Santa Claus. But a federal appeals court overturned her conviction last year and ordered a new trial, ruling that prosecutors withheld evidence of alleged misconduct by now-retired detective Armando Saldate – the key witness in the case.

Saldate claimed that Milke confessed, which she has always denied. Saldate was later found to have lied under oath or violated suspects’ rights during other interrogations, according to the 2013 court ruling.

“This was the witness in this case,” Judge Patricia Norris said at Tuesday’s court hearing.

With the help of her many supporters, Milke made bail and is free. But with the new trial looming, Milke’s attorneys hope to convince a three-judge panel that a second murder trial amounts to double jeopardy, meaning a defendant can't be tried a second time on the same charges after acquittal or conviction. Her argument failed to persuade a single-judge panel in January.

“The remedy is dismissal; it is to dismiss the charges,” her lawyer, Lori Voepel, said.

Prosecutors disagree, but neither side would elaborate after the hearing. Judges will rule in the coming weeks.

Saldate will be forced to testify again in the new trial.

ABC News Chief Legal Affairs Anchor Dan Abrams said given the skepticism surrounding Saldate’s testimony, the case against Milke has major flaws.

“The defense actually has a very weak argument on double jeopardy,” Abrams said. “It’s not double jeopardy to overturn a case and retry the defendant. The person’s getting a new trial.

“What the defense seems to be saying here is that the violations by the detective were so egregious that there shouldn’t be another trial.”